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| United States Patent |
5,604,515
|
|
Chen
|
February 18, 1997
|
Pulse-type driving device
Abstract
A pulse-type driving device for driving a plurality of light emitting
diodes includes a power source providing a DC voltage, a pointer control
circuit including a pulse output terminal for outputting pulses therefrom.
A plurality of sets of detecting circuits each of which includes one of
the light emitting diodes, a phototransistor, and a transistor. The light
emitting diode emits light to activate the phototransistor which in turn
triggers the transistor to output a signal to the pointer control circuit.
A constant current source is connected between the pointer control circuit
and the light emitting diodes and provides constant current to energize
the light emitting diodes.
| Inventors:
|
Chen; Chih-Cheng (San Chung, TW)
|
| Assignee:
|
Kye Systems Corp. (Taipei Hsien, TW)
|
| Appl. No.:
|
340591 |
| Filed:
|
November 16, 1994 |
| Current U.S. Class: |
345/163; 345/164; 345/166 |
| Intern'l Class: |
G09G 005/08 |
| Field of Search: |
345/163,164,166,167,211
178/18
|
References Cited
U.S. Patent Documents
| 4886941 | Dec., 1989 | Davis | 345/163.
|
| 4959805 | Sep., 1990 | Onouchi et al. | 178/18.
|
| 5027109 | Jun., 1991 | Donovan et al. | 345/165.
|
| 5153571 | Oct., 1992 | Takahashi | 345/163.
|
| 5298918 | Mar., 1994 | Yen-Chen et al. | 345/163.
|
| 5521617 | May., 1996 | Imai et al. | 345/167.
|
Primary Examiner: Hjerpe; Richard
Assistant Examiner: Mengistu; Amare
Attorney, Agent or Firm: Peterson, Wicks, Nemer & Kamrath, P.A.
Claims
I claim:
1. A pulse-type driving device for driving a plurality of light emitting
diodes comprising
a power source providing a DC voltage;
a pointer control circuit including a pulse output terminal for outputting
pulses therefrom;
a plurality of sets of detecting circuits each comprising one of said light
emitting diodes, a phototransistor, and a transistor, said light emitting
diode emits light to activate said phototransistor which in turns triggers
said transistor to output a signal to said pointer control circuit in
response;
a constant current source comprising a first transistor, a second
transistor and a resistor, a base of the first transistor connected to a
collector of the second transistor and the pulse output terminal of the
pointer control circuit for receiving pulses therefrom, an emitter of the
first transistor connected to a base of the second transistor, a collector
of the first transistor connected to the power source via the diodes of
the detecting circuits, said resistor connected between an emitter of said
first transistor and a ground;
whereby said first transistor and said second transistor are activated when
receiving a pulse from said pointer control circuit, in the mean time said
light emitting diodes are energized with a constant current determined by
a ratio between a base-emitter voltage of said second transistor and a
resistance of said resistor.
2. A pulse-type driving device as claimed in claim 1, wherein said first
transistor and said second transistor are NPN transistors.
3. A pulse-type driving device for driving a plurality of light emitting
diodes comprising
a power source providing a DC voltage;
a pointer control circuit including a pulse output terminal for outputting
pulses therefrom;
a plurality of sets of detecting circuits each comprising one of said light
emitting diodes, a phototransistor, and a transistor, said light emitting
diode emitting light to activate said phototransistor which in turns
triggers said transistor to output a signal to said pointer control
circuit in response;
a constant current source comprising a first transistor, a second
transistor and a resistor, a base of the first transistor connected to a
collector of the second transistor and the pulse output terminal of the
pointer control circuit for receiving pulses therefrom, an emitter of the
first transistor connected to a base of the second transistor, an emitter
of the first transistor connected to the power source via the resistor, an
emitter of the second transistor connected to the power source, a
collector of said first transistor connected to the diodes and said diodes
are connected to a ground;
whereby said first transistor and said second transistor are activated when
receiving a pulse from said pointer control circuit, in the mean time said
light emitting diodes are energized with a constant current determined by
a ratio between an emitter-base voltage of said second transistor and a
resistance of said resistor.
4. A pulse-type driving device as claimed in claim 1, wherein said first
transistor and said second transistor are PNP transistors.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pulse-type driving device, and more
particularly to one which is used in driving infrared diodes on a mouse or
track ball.
2. Description of the Prior Art
In a pointing input device such as a mouse or a track ball, photoelectric
components such as a pair of phototransmitter and photoreceiver are used
to detect displacement of the pointing input device in an X coordinate and
a Y coordinate. A conventional control circuit as shown in FIG. 5
comprises a pointer control circuit 70 which has four terminals XA, XB,
YA, YB respectively connected to one of four detecting circuit 80, 90, 80'
and 90' where two detecting circuits 80 and 90 are used for detecting
displacement along the X coordinate and two detecting circuits 80' and 90'
identical to the detecting circuits 80 and 90 are used for detecting
displacement along the Y coordinate. For example, the detecting circuit
for the X coordinate comprises two light emitting diodes 81, 91, two
phototransistors 82, 92 and two waveform-shaping transistors 83, 93. The
light emitting diodes 81, 91 and the phototransistors 82, 92 are
positioned at an opposite side to a photogrid wheel (not shown) thus
cooperating to detect the displacement in the X coordinate. Similarly, to
detect the displacement in the Y coordinate, another photogrid wheel is
provided to cooperate with the light emitting diodes 81', 91' and the
phototransistors 82', 92'
The collectors of the phototransistors 82, and 92 are connected to a power
source VCC. The emitters of the phototransistors 82, and 92 are
respectively connected to a base of the transistors 83 and 93. The
collectors of the transistors 83 and 93 are respectively connected to the
input terminals XA and XB of the pointer control circuit 70.
As described, as the mouse moves along the X coordinate, the corresponding
photogrid wheel also rotates, causing the phototransistors 82, 92 together
with the transistors 83 and 93 to output a corresponding number of pulses
to the input terminals XA, XB of the pointer control circuit 70, thus
providing X displacement signal to the pointer control circuit 70. A Y
displacement signal to the pointer control circuit 70 is similarly
provided.
From the above structure and description, it is known that the precision
for detecting the X displacement and the Y displacement depends on the
cooperation of the light emitting diodes 81, 91 and the phototransistors
82, 92, i.e., the illuminations of the two light emitting diodes 81, 91
should be identical, and the gains of the phototransistors 82, 92 have to
be identical. However, to obtain two phototransistors with identical gain
requires cumbersome testing procedure. In addition, the illumination from
the light emitting diodes 81, 91 has to be adjusted via a variable
resistor 84 connected to the diodes 81 and 91.
Since the efficiencies of the light emitting diodes may be different thus
affecting the precision of the detection of the phototransistors.
Additionally, the obtaining manner of the power source VCC may affect the
operative precision of the phototransistor. For example, a
serial-output-type mouse obtains a DC power directly from a signal
terminal of a serial interface RS-232C. However the signal levels for
different computers are not exactly the same thus causing variation on the
source voltage VCC and affecting the detecting precision of the
phototransistors. Alternatively, the mouse may obtain power source from a
computer connected thereto by using the same power supply of the computer.
In this case, the precision problem is raised when the mouse is connected
to a notebook computer. It is noted that the notebook computer uses
batteries as its power source thus the precision of the mouse is decreased
if the total voltage from the batteries reduces after long term use.
It is clear that the mouse suffers from an instability problem due to
insufficient voltage from the power supply and also suffers from a
precision problem due to parts difference such as the characteristic
difference of the phototransistors and the light emitting diodes.
The present invention has arisen to mitigate and/or obviate the
afore-described disadvantages of the conventional driving circuit.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide a pulse-type
driving device which provides constant current to drive infrared diodes on
a mouse or track ball thus insuring the mouse or the track ball functions
in a stable condition.
In accordance with one aspect of the invention, there is provided a
pulse-type driving device for driving a plurality of light emitting diodes
including a power source, a pointer control circuit including a pulse
output terminal for outputting pulses therefrom. A plurality of sets of
detecting circuits each includes one of the light emitting diodes, a
phototransistor, and a transistor. The light emitting diode emits light to
activate the phototransistor which in turn triggers the transistor to
output a signal to the pointer control circuit. A constant current source
is connected between the pointer control circuit and the light emitting
diodes and provides constant current to energize the light emitting
diodes.
Further objectives and advantages of the present invention will become
apparent from a careful reading of the detailed description provided
hereinbelow, with appropriate reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram in accordance with the present invention;
FIG. 2 is a characteristic chart of a phototransistor;
FIG. 3 is an alternative embodiment of the constant current circuit in
accordance with the present invention;
FIG. 4 is an alternative embodiment of the constant current circuit in
accordance with the present invention; and
FIG. 5 is a conventional driving circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a pulse-type driving device in accordance with the
present invention comprises a pointer control circuit 10, four sets of
detecting circuits 20, and a constant current source 30. The four sets of
detecting circuit 20 each comprising a light emitting diode 21, a
phototransistor 22, and a transistor 23 are conventional and identical to
those described previously, thus they are not described in more detail.
The pointer control circuit 10 comprises four input terminals XA, XB, YA,
YB exactly identical to a conventional one. The pointer control circuit 10
further comprises a pulse output terminal XOUT for outputting pulses in
response to the input to the input terminals XA, XB, YA, YB thereof.
The feature of the present invention is in the constant current source 30.
The constant current source 30 is coupled to the output terminal XOUT or
an output terminal OUT of the pointer control circuit 10. The frequency of
the pulses outputted from the output terminal XOUT may be ranged from
thousands to millions of hertz. The duty cycle of the pulses may be
adjusted according to operation requirement. The constant current source
30 comprises a first transistor 31 and a second transistor 32, with a base
of the first transistor 31 connected to a collector of the second
transistor 32, and an emitter of the first transistor 31 connected to a
base of the second transistor 32. The first transistor 31 has a collector
connected to a power source VCC via two diodes 21. The base of the first
transistor 31 and the collector of the second transistor 32 are connected
to the output terminal XOUT of the pointer control circuit 10 via a
resistor 38. Alternatively, the base of the first transistor 31 and the
collector of the second transistor 32 may be connected to an output
terminal OUT of the pointer control circuit 10 via the resistor 38.
The first transistor 31 is turned on when a positive cycle of the pulse
from the output terminal XOUT of the pointer control circuit 10 is applied
to the base of the first transistor 31. It is known that the first
transistor 31 is an NPN transistor, thus it is turned on when a positive
voltage is applied on the base thereof. The diodes 21 are immediately
energized to illuminate after the first transistor 31 is turned on. It is
known that a loop from the power source VCC through the light emitting
diodes 21, the first transistor 31, the resistor 33 and ground is formed
to energize the light emitting diodes 21 to illuminate when the transistor
31 is turned on. A forward current I.sub.F of the energized diodes 21 is
determined by a voltage drop V.sub.BE between the base and emitter of the
second transistor 32. It is clearly understood that the forward current
I.sub.F through the diodes 21 is substantially equal to a current through
the resistor 33. In the present embodiment, the current I.sub.F through
the resistor 33 is equal to the base-emitter voltage drop V.sub.BE divided
by the resistance of the resistor 33, i.e., I.sub.F =V.sub.BE /R.sub.E,
where R.sub.E represents the resistance of the resistor 33. In this
configuration, the forward current through the diodes 21 remains in a
substantially constant value even when the power source VCC changes.
Therefore, it is appreciated that the configuration of the constant
current source 30 of the present invention provides a stable operation
current to illuminate the diodes 21. Therefore, the illumination from the
diodes 21 remains in a substantially constant value.
FIG. 2 illustrates a characteristics curve for a phototransistor 22, where
a collector current I.sub.C of the phototransistor 22 is substantially
proportional to an illumination E.sub.e from the light emitting diodes 21
onto the phototransistor 22. The collector current I.sub.C of the
phototransistor 22 can be limited in a required range if the illumination
E.sub.e of the light emitting diode 21 is controlled in a specific range.
From the above description, it is understood that the constant current
source 30 of the present invention enables the light emitting diodes 21 to
operate with a stable current, which in turn causes the phototransistor 22
to function with a stable collector current. Therefore, the constant
current source 30 can solve the precision problem caused by power supply
instability in a notebook computer or the like. It is known that the
allowable voltage range is from 3 to 6 volts.
In the previous embodiment, the first transistor 31 and the second
transistor 32 are NPN type transistors and the first transistor 31 may be
activated by applying a positive pulse on the base thereof. An alternative
embodiment of the constant current source 30 as shown in FIG. 3 comprises
a third transistor 34 and a fourth transistor 35, where the transistors 34
and 35 are PNP type transistors and the third transistor 34 is activated
by a logical low half cycle of the pulse from the pointer control circuit
10. The base of the third transistor 34 is connected to the collector of
the fourth transistor 35 and the emitter of the third transistor 34 is
connected to the base of the fourth transistor 35. A resistor 36 is
connected between the emitter of the third transistor 34 and the emitter
of the fourth transistor 35. Therefore, a current I.sub.F which passes
through the diodes 21 is also determined by the base-emitter voltage
V.sub.BE of the transistor 35 and the resistance R.sub.E of the resistor
36, where I.sub.F =V.sub.BE /R.sub.E.
FIG. 4 illustrates an alternative embodiment of the pulse-type driving
device in accordance with the present invention. The constant current
source 30 is identical to the one shown in FIG. 3, except that the
resistor 36 is replaced with resistor 33. The four detecting circuits 20
are replaced with two detecting circuits 40 each of which comprises a
light emitting diode and two phototransistors. In this embodiment, the
current I.sub.F through each diode is determined by V.sub.BE divided by
R.sub.E, where V.sub.BE is the base-emitter voltage of the transistor 35
and R.sub.E is the resistance of the resistor 33. The detecting circuit 40
is commercially available.
While the present invention has been explained in relation to its preferred
embodiment, it is to be understood that various modifications thereof will
be apparent to those skilled in the art upon reading this specification.
Therefore, it is to be understood that the invention disclosed herein is
intended to cover all such modifications as fall within the scope of the
appended claims.
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